1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a method of fabricating a vertical thin film transistor (vertical TFT).
2. Description of the Related Art
As a newly emerged technique today, a lightweight, ultra-thin, portable and flexible display, such as an electronic paper (e-paper; e-ink), has attracted more attention of customers than ever before. Meanwhile, many manufacturers follow such development train one after another. The organic thin film transistor (OTFT) is a TFT suitable for varied electronic products by adopting an organic molecular material. The most remarkable advantage of an OTFT resides in it can be fabricated under a lower temperature and retain the designed characteristic of a transistor device to obtain the normal display quality. Along with the widespread applications of OTFTs, the flexible electronic products, such as the flexible displays, are expected to share more market soon.
The advantage of an OTFT in vertical structure resides in a higher mobility thereof, friendliness to the higher frequency applications and a lower operation bias voltage. However, the OTFT in vertical structure is difficult to be fabricated. By using the conventional semiconductor process to fabricate an OTFT device in vertical structure, normally, multiple coating processes and multiple patterning processes are conducted, which requires multiple masks. Such a complex fabrication process tends to increase the production cost. In particular, the characteristic of the organic semiconductor after a photolithography process, which makes the fabricated OTFT in vertical structure fail to retain the expected good characteristic.